In a dry climate, ladder line is fine, but good coax has low losses, too, and is less fussy about being run next to the gutters.
It is rare for a dipole to be perfectly balanced (thanks to near field objects like houses), so a high-quality current balun at the antenna can really help reject common mode noise. I recommend Balun Designs. Mine dropped the noise by 6dB. Also consider the “loop skywire”. A loop often fits into the same space as a dipole and lots of people like them. For pre-built dipoles, I’m happy with my Hy Power Antenna: http://www.hypowerantenna.com/ wunder K6WRU CM87wj http://observer.wunderwood.org/ On Oct 17, 2014, at 6:35 PM, James Bennett <[email protected]> wrote: > Fred is right about the 450-ohm stuff getting funky in wet weather. Cause my > tuners to do the clicky-click dance whenever it rains here, although we've > been pretty dry the past few years. Because of this, I plan on replacing my > 450-ohm line with 600-ohm ladder line in a couple weeks. I had the 600-ohm > stuff on that doublet initially but a change in roofing materials made me > change. Long story. Anyway, as you probably know, antennas work much better > when built or adjusted when the weather is horrible!!! > > Jim / W6JHB > > >> On Oct 17, 2014, at 4:57 PM, Fred Jensen <[email protected]> wrote: >> >> Don pretty much described my low band antenna. Full Disclosure: I live on 5 >> acres and have a 70' tower. That said, it is a Sloping V [I'd call it an >> inverted V except is isn't resonant on any band], about 210' on a side from >> the top of the tower. 450 ohm window line to the bottom of the tower, DXE >> 4:1 balun, and coax into the house. I have chokes on the coax at the balun >> and at the weatherhead entrance, but I've never had any problems with RFITS >> [RF In The Shack] with or without the chokes. >> >> It works well on 80-40-30, requires a tuner of course [KAT500]. Works on >> 160 but warms the clouds and worms, I use an Inv-L for top band. It also >> works on all the bands up from 30 but the pattern gets fairly complex and >> squirts my RF in a lot of non-productive directions because it's so big. >> >> My experience is that an 88 ft doublet, center-fed, works really well on 40 >> and up in frequency, often used by those activating summits in Summits On >> The Air. Shorter doublets are also effective, and not being resonant >> doesn't really matter [in some cases, it helps]. Neither does what you do >> with the ends. Most of the radiation comes from the center, high current >> sections. >> >> 450 ohm window line is sensitive to moisture ... if you set up your tuner >> for dry conditions and it's now raining, things will need retuning. >> >> Keep in mind the wisdom of Tom, N6BT, "Anything conductive will radiate if >> you get power into it." >> >> 73, >> >> Fred K6DGW >> - Northern California Contest Club >> - CU in the 2015 Cal QSO Party 3-4 Oct 2015 >> - www.cqp.org >> >>> On 10/17/2014 3:54 PM, Don Wilhelm wrote: >>> >>> Make it a balanced dipole antenna (equal lengths on either side of the >>> feedpoint) for best efforts in keeping RF off the feedline. The actual >>> length does not matter a lot, but it should be greater than 80% of the >>> half wavelength for the lowest band of interest. >>> >>> Use open wire line or 450 ohm ladder line to feed it down to the point >>> where it enters the shack - hopefully you can run the feedline >>> perpendicular from the radiator for at least 1/4 wavelength on the >>> lowest frequency of interest for lowest radiator to feedline pickup. Put >>> a good 1:1 current mod choke at that point. See page 29 of K9YC's RFI >>> tutorial http://www.audiosystemsgroup.com/RFI-Ham.pdf >>> for instructions on how to construct a very effective current mode choke >>> - note: a good balun *is* a current mode choke, but many fail to perform >>> as well as the ones tested by K9YC. >>> >>> You will need a tuner, and any Elecraft tuner should do the job nicely. >>> If it does not, then you may have to make some adjustments in the length >>> of the parallel feedline to see if you can achieve success on all bands >>> of interest. >>> >>> You may want to take a look at the Antenna and Transmission Line article >>> on my website www.w3fpr.com for a bit on non-math theory on antennas. >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
